Deemed worthy of becoming the champion of the ancient wizard Shazam, whenever he utters the word "Shazam" young Billy Batson is struck by a magical thunderbolt and gains the powers and abilities of Solomon, Hercules, Atlas, Zeus, Achilles, and Mercury, as well as transforming him into the World's Mightiest Mortal, SHAZAM!

@justanormalguy: In Trials of Shazam, Billy took Shazam's stead as Lord Marvel. Making the position of Captain Marvel open. Freddy took on a role of quests to become Shazam. During one of the trials he summoned the power of Shazam via his will. So he could say the name and it wouldn't strike him, but he could will it to come and the bolt would strike.